(1) Field of the Invention
The present invention relates to a continuous medium printing apparatus for printing data to be printed on a continuous medium such as a continuous recording paper by using an electrophotograph, for example.
(2) Description of Related Art
There are known several kinds of systems in which image data is printed on a continuous medium (hereinafter sometimes referred to as continuous paper or simply paper). One of these system, or an electrophotograph system is very popular because of its low cost.
FIG. 46 is a schematic diagram of a continues medium printing apparatus in which an electrophotograph system is employed. As shown in FIG. 46, data to be printed sent from an upper controller unit 93 is supplied to a mechanism control unit 91 provided within a printer 90, in which the data to be printed is transferred to a photosensitive body drum (photosensitive drum) 90e by an exposing unit 90d. In this case, the photosensitive drum 90e is rotated in the clockwise direction in FIG. 46. Initially, the photosensitive drum 90e has charged its surface uniformly by a pre-charging device 90c. When the photosensitive drum 90e is exposed under light by the exposing unit 90d, then an electrostatic latent image corresponding to the data to be printed is formed on the surface of the photosensitive drum 90e. The electrostatic latent image is developed by a developing device 90g so as to form a toner image. The toner image on the surface of the photosensitive drum 90e is transferred to the paper by means of a transfer electrifying device 90f and a conveying body 30i.
Thereafter, residual toner is removed by a cleaner unit 90b. The photosensitive drum 90e has again its surface electrified uniformly by the pre-charging device 90c so that the photosensitive drum 90e can cope with the next step of transfer process. Meanwhile, continuous paper 92 is conveyed by a conveying tractor (paper conveying mechanism) 90h. When the paper reaches a place beneath a fixing device 90a, the transferred toner image is fixed by heat applied by the fixing device 90a. The paper printed with the image thereon is reserved within a continuous paper reserving unit.
When the printer 90 prints data to be printed supplied from the upper controller unit 93, sometimes a print image drop, a dirt spot or the like occurs due to a folding portion of the continuous paper 92. Therefore, it is necessary for an operator of the printer to check the printed image so that the printing operation can be continued or the dirt spot or the like can be detected even if the image drop or the dirt spot is caused in the printed image.
To this end, there has been proposed an apparatus in which an image having been printed on the continuous paper is read by a reading apparatus, and the printed image data read by the reading apparatus and data to be printed are compared with each other. According to the apparatus, comparison is made by detecting the correspondence between the predetermined paper size and the data to be printed. Proposes with regard to the apparatus can be found in the following five kinds of publications.
Initially, in Japanese Patent Laid-Open Publication No. HEI 7-81191 (hereinafter referred to as a publication 1), there is disclosed a printer equipped with a print result comparing function by which it is determined automatically and at a high speed, whether the printer produced a print result correctly or not. According to the technology disclosed in the publication 1, the printer includes a picked-up area designating means 32 by which an area to be compared with data to be printed is designated from data read as printed image data. The data of the area designated by the picked-up area determining means 32 is recognized as picked-up characters and subjected to the comparison.
In Japanese Patent Laid-Open Publication No. HEI 6-237350 (hereinafter referred to as a publication 2), there is disclosed a facsimile apparatus in which when printing error is detected, causing an error, only the page containing the error is again printed so that the print error is recovered. According to the technology disclosed in the publication 2, the printed text data is read by some device provided in the facsimile apparatus, subjected to check, and a print retrying request is issued on the page containing the error so that printing of the page is retried.
Next, in Japanese Patent Laid-Open publication No. HEI 9-216441 (hereinafter referred to as publication 3), there is disclosed an image defect detecting apparatus in which a defect of a printed image can be positively detected with a short period of time. According to the technology disclosed in the publication 3, image data extracted on the basis of position information about an important area out of image data read in an optical manner, is subjected to comparison with original image data offered to printing, and if it is determined that both the data are not coincident to each other, a defect detecting signal is generated. In this case, there are introduced three methods for attaching the position information of the important area. That is, a method in which a position information is registered in advance, a method in which image data to be attached with the position information is extracted from Page Description Language, and a method in which a shading composed of code information containing the position information of the important area is detected so that it is determined whether the shading of the image is dropped or not.
Further, in Japanese Patent Laid-Open Publication No. HEI 3-36071 (hereinafter referred to as a publication 4), there is disclosed a printer apparatus in which printed result and print data are compared with each other so that error printing can be detected. According to a phase difference control circuit introduced in the publication 4, control is carried out by taking into account the correction on a time it takes for a paper to travel from a printing position to a data reading device. In this way, print error can be detected and reliability in printing operation can be guaranteed at a very high level.
Furthermore, in Japanese Patent Laid-Open Publication No. HEI 8-25764 (hereinafter referred to as a publication 5), there is disclosed a printer apparatus in which print error can be corrected solely by the printer apparatus and number of times of print retrying is restricted. According to the technology disclosed in the publication 5, print error can be corrected in the printer apparatus, so that load of error processing imposed on an apparatus governing the printer apparatus is relieved and efficiency of channels is improved so that error correction process can be carried out for a short period of time. Moreover, the printer apparatus is provided with a counter for restricting the number of times of print retrying so that time consumption in the print retrying is limited to a predetermined level.
Incidentally, when printing is carried out on continuous paper by using these printer apparatus, these printers are placed in a situation in which a plurality of printers are connected to a single printer line so that each printer prints on paper of a different size at a different resolution. Further, data to be printed sent from a controller unit governing the printer apparatus is printed continuously by the plurality of printers. Furthermore, a single printer can print the data on paper of a plurality of sizes at a plurality of resolution levels. Therefore, according to the technologies disclosed in the publications 1 to 5, when each of the plurality of printers prints the data on paper of each different size at each different resolution level, comparison between the data to be printed and actually printed data cannot be carried out in accordance with the paper size and resolution level in each printer.
In addition to the above drawback, when so called loading operation is carried out, i.e., continuous paper is loaded in the printer and the comparing unit, it is necessary for an operator of the apparatus to count the number of pages of the continuous paper placed between the printer and the comparing unit, which fact is a cumbersome operation for the operator. For this reason, there has been proposed a method in which a printer prints a control mark on an area outside a printing area of a printing face of the continuous paper, the comparing unit recognizes the position of the control mark, and a unit of page of the printing face is determined.
According to the above-described method, a mechanism control unit 91 (see FIG. 46) creates data of the control mark, and printing is carried out by synthesizing the data of the control mark and the data to be printed sent from an upper controller unit 93. In this method, if the data to be printed is transmitted to a comparing unit, it becomes possible to compare printed image data read by some device with the data to be printed. However, according to the above method, the data to be printed sent to the comparing unit is added with the data of the control mark by the mechanism control unit 91. Therefore, if some trouble is caused in the mechanism control unit 91, the data to be printed sent to the comparing unit becomes coincident with data having been printed on the continuous paper, which makes it impossible to detect erroneous printing.
On the other hand, there has been proposed a technology in which an operator can settle an allowable level of print quality. That is, the allowable level serves as the degree of allowable defect when detecting the print defect upon comparing the data with each other. The allowable level is variably settled in advance by the operator depending on the degree of importance of the print job. When print defect is detected, the printer selects one of operations, i.e., the printer is instantly stopped and the printer is stopped when a number of pages containing unsatisfactory printing reaches a predetermined number, depending on the setting of the operator.
According to the technology, however, it is necessary for the operator to settle the allowable level for each print job. Therefore, if the setting of the allowable level is erroneously carried out, the comparing unit of the printer can immediately stop upon detection of the print defect. Further, continuous printing can be carried out in spite of the fact that the operator desires to carry out print retrying operation. Conversely, print defect is detected, leading to instant stop of the printer, in spite of the fact that the operator dose not want to stop the print operation. In this way, some drawbacks can be expected.
Further, according to a prior art technology, when the comparing unit compares data to be printed with the print image data to detect a print defect, even if the comparing unit suffers from any trouble and print defect is detected, the printer is not informed of the fact. Thus, the printer continues to print while the print defect is left uncorrected.
In addition to the above drawback, according to the prior art technology, paper conveying control on the side of the printer and paper conveying control on the side of print comparing unit are made synchronous with each other. Therefore, it becomes difficult to carry out accurate print comparing operation regarding a page at which print comparing operation is stopped.
FIG. 47 is a diagram showing the paper conveying speed of the printer in which the paper conveying speed of the printer is made synchronous with the paper conveying speed of the print comparing unit. In FIG. 47, time is plotted in abscissa while speed (millimeter per second) is plotted in ordinate. The speed is positive in the area above the abscissa. Reference symbols P1, P2, P3 and P4 in FIG. 47 are sampled points of timing.
An interval between the reference symbols P1 and P2 in FIG. 47 is an interval in which paper is conveyed in the print conveying direction (paper conveying direction) and operations of reading and comprising are carried out. If print operation is stopped in an interval between the reference symbols P2 and P3, reading operation is carried out from the timing point P3 at which paper has been conveyed by a distance between the printer and the print comparing unit. However, the result becomes uncertain, with the result that the print comparing operation is stopped in a halfway of a page. Then, if printing is resumed, then reading is started. Therefore, accurate print comparing operation is not carried out about the page in which print comparing operation is stopped.